Land cover change analysis has been an active area of research in the remote sensing community for many years. The idea is to make computational protocols and algorithms that take a couple of digital images collected by satellites or airplanes, turn them into land­cover maps, layer them on top of each other, and pick out the places where the land cover type has changed. The best protocols are the most precise, the fastest, and which can chew on multiple images recorded under different conditions. One of the favorite applications of land cover change analysis has been deforestation detection. A particularly popular target for deforestation analysis is the tropical rain forests, which are being chain sawed down at rates which are almost as difficult to comprehend as it is to judge exactly how bad the effects of their removal will be on biological diversity, planetary ecosystem functioning and climate stability.

Google has now gotten itself into the environmental remote sensing game, but in a Google-esque way: massively, ubiquitously, computationally intensively, plausibly benignly, and with probable long-term financial benefits. They are now running a program to vacuum up satellite imagery and apply land cover change detection optomized for spotting deforestation, and for the time being targeted at the Amazon basin. The public doesn’t currently get access to the results, but presumably that access will be rolled out once Google et al are confident in the system. I have to hand it to Google: they are technically careful, but politically aggressive. Amazon deforestation is (or should still be) a very political topic.

[Editor's note: It's been a while since I've seen gradient country fills (!) on a map but this month's Wired magazine obliges with their highly stylized map of piracy off the Somalia coast. The Flash version of the print graphic has a nifty approach to panning the zoomed image, but beyond the novelty is not an effective navigation tool, especially with the single zoom in level.]

Most of Somalia’s modern-day pirates are fisherman who traded nets for guns. They’ve learned that ransom is more profitable than robbery, and rather than squandering their loot, they reinvest in equipment and training. Today, no ship is safe within several hundred miles of the coast.

Inbound JFK. The turns start while you’re still in the clouds. Engines howling, flaps down, the plane lurches and dives, jerky as a taxi in Midtown. Seatback upright and tray table locked, you’re oblivious to the crowded flight paths around you. But the air above New York City is mapped: a dense and nuanced geography nearly as complicated as the city below.

More than 2 million flights pass over the city every year, most traveling to and from the metropolitan area’s three busiest airports: John F. Kennedy, Newark, and LaGuardia. And all that traffic squeezes through a network of aerial routes first laid out for the mail planes of the 1920s. Aircraft are tracked by antiquated, ground-based radar and guided by verbal instructions issued over simplex radios, technology that predates the pocket calculator. The system is extremely safe—no commercial flight has been in a midair collision over the US in 22 years—but, because the Federal Aviation Administration treats each plane as if it were a 2,000-foot-tall, 6- by 6-mile block lumbering through the troposphere, New York is running out of air.

This is a nightmare for New York travelers; delays affect about a third of the area’s flights. The problem also ripples out to create a bigger logjam: Because so many aircraft pass through New York’s airspace, three-quarters of all holdups nationwide can be traced back to that tangled swath of East Coast sky.

Six years ago, Congress green-lit a plan to solve this problem. The Century of Aviation Reauthorization Act calls for a new system, dubbed NextGen, that uses GPS to create a sort of real-time social network in the skies. In theory, it should give pilots the data they need to route themselves—minus the huge safety cushions.

But NextGen needs some serious hardware: roughly $300,000 in new avionics equipment for every cockpit. That’s a lot of peanuts for the struggling airlines. Add to the tab nearly 800 new federally funded ground stations to relay each plane’s location and trajectory to every other plane in the sky and—by the time NextGen finally launches in 2025—the price tag could reach $42 billion.

Jetliner Photos: Jeffrey Milstein

In the meantime, the New York-area skies have seen a huge traffic bump over the past two decades—including a 48 percent increase between 1994 and 2004. So the FAA has set out to coax new efficiency from old technology.

To help reorganize this airspace, the FAA called on Mitre, a Beltway R&D firm that works exclusively for the government. Mitre’s scientists and mathematicians, in cooperation with some of the region’s air traffic controllers, are completely rethinking the flow of aircraft in and out of New York City. Current flight patterns evolved like a rabbit warren, with additions tacked on to an existing architecture. As airports grew busier and airplanes started flying higher and faster, that architecture became increasingly inefficient. The plan, the unfortunately named New York/New Jersey/Philadelphia Metropolitan Area Airspace Redesign, aims to bring order to the air.

Think of it as a redrawn map of the roadways in the sky. While planes used to chug in and out of the city on a few packed roads, the redesign spreads out the aircraft by adding new arrival posts (exit ramps), departure gates (on-ramps), and takeoff headings (streets leading up to the intercity highways). But the biggest move will be making the space for all these additions. Mitre’s proposal is to extend the boundaries of this airborne city into a 31,180-square-mile area that stretches from Philadelphia to Albany to Montauk.

Unclogging the Skies

A new FAA plan—the New York/New Jersey/Philadelphia Metropolitan Area Airspace Redesign—aims to streamline the air traffic over New York. Here are two highlights.

Adding Lanes
Flights heading west out of New York have to squeeze onto two airborne highways over New Jersey before they merge with air traffic from the rest of the country. The redesign adds more lanes, allowing more planes to take off per hour.

Expanding Control
The New York regional air traffic control center is the busiest in the world. The redesign integrates its authority with other regional centers so controllers can direct planes that are farther away, clearing the high-altitude flight paths for through-traffic

The FAA started implementing the first part of the plan—the new takeoff headings—in December 2007 and should have the full strategy in place by 2012. By then the agencies hope to have reduced delays in New York by an average of three minutes per flight. And in a system as interconnected as the US air traffic network, those few minutes could quickly cascade into hours.

Sure, the world is complicated, but not as complicated as you might think. It turns out that most organic molecules—the kind of chemicals that make food tasty, perfumes fragrant, and life alive—derive from a few relatively simple architectures.

Together with a bunch of data-minded colleagues, Alan Lipkus of the Chemical Abstracts Service took a deep dive into his organization’s century-old library of 24 million organic compounds—most of them synthetic. They found that more than half are built from just 143 basic shapes, or “frameworks.” And the rest? Well, building those requires the other 836,565 cataloged frameworks.

Why do a handful of fundamental shapes get all the work? In part because chemists typically create new molecules—in the search, say, for potential new drugs—from the ones they’re familiar with. It’s cheaper. But Lipkus hopes that showcasing this lopsided approach will encourage researchers to work farther out on the long tail of molecular geometry. “A lot of structures have not been fully explored,” he says. “There could be interesting things to discover.” Here’s a snapshot of the newly discovered shape-alphabet.

Top 30 Molecular Shapes

Molecules are clusters of atoms joined like Tinkertoys. The range of possible structures is vast, but they can all be categorized by “molecular framework”—the underlying rings and connectors. Most common by far is the hexagon—a ring of six atoms, with one at each corner, that’s the basis for nearly 10 percent of known organic compounds. Here are the top 30 most common frameworks, with frequency of occurrence in parentheses.

Republished from Wired.
By Eliot Van BuskirkOriginally published January 30, 2009

Entrepreneur Mark Gorton wants to do for people what he already helped do for files: move them from here to there in the most efficient way possible using open-source tools.

Gorton, whose LimeWire file sharing software for the open-source gnutella network was at the forefront of the P2P revolution nearly a decade ago, is taking profits earned as a software mogul and spinning them into projects to make urban transportation safer, faster and more sustainable.

You might call it a “P2P-to-people” initiative — these efforts to make cities more people-friendly are partly funded by people sharing files.

That’s not the only connection between open-source software and Gorton’s vision for livable cities. The top-down culture of public planning stands to benefit by employing methods he’s lifting from the world of open-source software: crowdsourced development, freely-accessible data libraries, and web forums, as well as actual open-source software with which city planners can map transportation designs to people’s needs. Such modeling software and data existed in the past, but it was closed to citizens.

Gorton’s open-source model would have a positive impact on urban planning by opening up the process to a wider audience, says Thomas K. Wright, executive director of the Regional Plan Association, an organization that deals with urban planning issues in the New York metropolitan area.

“99 percent of planning in the United States is volunteer citizens on Tuesday nights in a high school gym,” Wright says. “Creating a software that can reach into that dynamic would be very profound, and open it up, and shine light on the decision-making. Right now, it becomes competing experts trying to out-credential each other in front of these citizen and volunteer boards… [Gorton] could actually change the whole playing field.”

Portland, Oregon has already used his open-source software to plan its bus routes. San Francisco, whose MUNI bus system is a frequent target of criticism, could be next to get the treatment. Gorton says he’s in talks with the city to supply transit routing software for MUNI that will do a much better job of keeping track of where people are going and figuring out how best to get them there. San Francisco “overpaid greatly” for a badly-supported proprietary closed-source system that barely works, according to Gorton, putting the city under the thumb of a private company that provides sub-par support.

“They’re frustrated and thinking about replacing it completely, and see the value of open-source because then they won’t have any of these support problems,” he said. “And they won’t be constantly at the mercy of the private companies that have these little mini-monopolies.”

The Open Planning Project (TOPP) was Gorton’s first foray into urban planning, in 1999. It initially involved an ambitious plan to use open-source software to model public transportation and traffic systems in large cities.

“I was much more naive at the time,” he said. “I thought, ‘I can make software. I’ll go build an open-source traffic and transportation model, which will show how much better things can be, and then go magically adopt those solutions.”

But humans can be harder to program than machines, and sometimes a human-to-human interface works best. “We’ve actually been incredibly successful transforming policy in New York City without any models at all,” he added, though some residents complained about parking spaces morphing into bike lanes.

The quest to bring open-source software to real-world urban planning continued, following the clearance of a key hurdle: Before you can build a transportation model, you need to know where the roads are.

While public, that data was locked by private software used by public organizations and suffered from an overall lack of standards. Thus was born GeoServer, an open-source, Java-based software server that lets anyone view and edit geo-spatial data. Road information can now be painstakingly imported once from proprietary systems or entered from scratch, double-checked by other users, and rolled out to anyone who needs the data.

“It didn’t really exist before,” said Gorton. “Most of the data was run on software from a company called ESRI. Government agencies have this data, but it’s all running on proprietary systems and you couldn’t get access to it, or it was very hard to get access to it.” GeoServer now runs in thousands of places around the world for all sorts of reasons, according to Gorton, whenever an online app needs to know where roads are.

[Editor’s note: Anyone concerned about geotagging and privacy should read this informative article from Wired Magazine. Author Mathew Honan became a geo-guinea pig by geotagging his entire life for a couple weeks and posting it live all his social networking site. Read about his experience’s pros and cons. It might just change your life.]

I’m baffled by WhosHere. And I’m no newbie. I built my first Web page in 1994, wrote my first blog entry in 1999, and sent my first tweet in October 2006. My user number on Yahoo’s event site, Upcoming.org: 14. I love tinkering with new gadgets and diving into new applications. But WhosHere had me stumped. It’s an iPhone app that knows where you are, shows you other users nearby, and lets you chat with them. Once it was installed and running, I drew a blank. What was I going to do with this thing?

So I asked for some help. I started messaging random people within a mile of my location (37.781641 °N, 122.393835 °W), asking what they used WhosHere for.

My first response came from someone named Bridget, who, according to her profile, at least, was a 25 year-old woman with a proclivity for scarves. “To find sex, asshole,” she wrote.

“I’m sorry? You mean it’s for finding people to have sex with?” I zapped back.

“Yes, I use it for that,” she wrote. “It’s my birthday,” she added.

“Happy birthday,” I offered.

“Send me a nude pic for my birthday,” she replied.

A friendly offer, but I demurred. Anonymous geoshagging is not what I had in mind when I imagined what the GPS revolution could mean to me.

The location-aware future—good, bad, and sleazy—is here. Thanks to the iPhone 3G and, to a lesser extent, Google’s Android phone, millions of people are now walking around with a gizmo in their pocket that not only knows where they are but also plugs into the Internet to share that info, merge it with online databases, and find out what—and who—is in the immediate vicinity. That old saw about how someday you’ll walk past a Starbucks and your phone will receive a digital coupon for half off on a Frappuccino? Yeah, that can happen now.

Simply put, location changes everything. This one input—our coordinates—has the potential to change all the outputs. Where we shop, who we talk to, what we read, what we search for, where we go—they all change once we merge location and the Web.

I wanted to know more about this new frontier, so I became a geo-guinea pig. My plan: Load every cool and interesting location-aware program I could find onto my iPhone and use them as often as possible. For a few weeks, whenever I arrived at a new place, I would announce it through multiple social geoapps. When going for a run, bike ride, or drive, I would record my trajectory and publish it online. I would let digital applications help me decide where to work, play, and eat. And I would seek out new people based on nothing but their proximity to me at any given moment. I would be totally open, exposing my location to the world just to see where it took me. I even added an Eye-Fi Wi-Fi card to my PowerShot digital camera so that all my photos could be geotagged and uploaded to the Web. I would become the most location-aware person on the Internets!

The trouble started right away. While my wife and I were sipping stouts at our neighborhood pub in San Francisco (37.770401 °N, 122.445154 °W), I casually mentioned my plan. Her eyes narrowed. “You’re not going to announce to everyone that you’re leaving town without me, are you? A lot of weirdos follow you online.”

Sorry, weirdos—I love you, but she has a point. Because of my work, many people—most of them strangers—track my various Flickr, Twitter, Tumblr, and blog feeds. And it’s true; I was going to be gone for a week on business. Did I really want to tell the world that I was out of town? It wasn’t just leaving my wife home alone that concerned me. Because the card in my camera automatically added location data to my photos, anyone who cared to look at my Flickr page could see my computers, my spendy bicycle, and my large flatscreen TV all pinpointed on an online photo map. Hell, with a few clicks you could get driving directions right to my place—and with a few more you could get black gloves and a lock pick delivered to your home.

To test whether I was being paranoid, I ran a little experiment. On a sunny Saturday, I spotted a woman in Golden Gate Park taking a photo with a 3G iPhone. Because iPhones embed geodata into photos that users upload to Flickr or Picasa, iPhone shots can be automatically placed on a map. At home I searched the Flickr map, and score—a shot from today. I clicked through to the user’s photostream and determined it was the woman I had seen earlier. After adjusting the settings so that only her shots appeared on the map, I saw a cluster of images in one location. Clicking on them revealed photos of an apartment interior—a bedroom, a kitchen, a filthy living room. Now I know where she lives.

You might think that your iPhone triangulates its location by using multiple cell towers, but it actually needs only one. After identifying the single nearby tower that it’s pinging, the iPhone queries a database at Google that lists the location of cell towers. That information is sent back to your phone, telling the device approximately where it is.

Pros: Very fast. Works anywhere you have a cell signal, including inside.Cons: Accurate enough to find restaurants, but not for directions.

Wi-Fi

Accuracy: 30 meters

The iPhone can also pinpoint its location using Wi-Fi. A company called Skyhook cruises cities to map the location of Wi-Fi nodes. The iPhone sniffs them out, measures their signal strength, and reports back to Skyhook’s servers. Based on its database, Skyhook computes where you must be to have that particular pattern of signal strengths.

Pros: Fast. Surprisingly accurate if you’re in an area with high network density.Cons: Useful only in urban areas with lots of Wi-Fi networks.

GPS

Accuracy: 10 meters

GPS satellites orbit Earth, constantly broadcasting an identification signal, their location in space, and the time on their atomic clock. The iPhone uses assisted GPS, which means it can tap into an assistance server and a reference network, helping to get a more accurate GPS reading more quickly.

Pros: By far the most accurate location system available.Cons: Although A-GPS is much faster than conventional, it’s still rather slow. And because it requires a view of the sky, it doesn’t work indoors or in built-up urban areas.

Geo-enthusiasts will assure you that these privacy concerns are overplayed: Your cell phone can be used to pinpoint your location anyway, and a skilled hacker could likely get that data from your mobile carrier. Heck, in the UK, tracking mobile phone users is as simple as entering their number on a Web site (as long as they give permission). But the truth is, there just aren’t that many people who want to prey on your location. Still, I can’t help being a little skittish when I start broadcasting my current position and travel plans. I mean, I used to stop newspaper delivery so people wouldn’t realize I was out of town. Now I’ve told everyone on Dopplr that I’m going to DC for five days.

And location info gets around. The first time I saw my home address on Facebook, I jumped—because I never posted it there. Then I realized it was because I had signed up for Whrrl. Like many other geosocial applications, Whrrl lets you cross-post to the microblogging platform Twitter. Twitter, in turn, gets piped to all sorts of other places. So when I updated my location in Whrrl, the message leaped first to Twitter and then to Facebook and FriendFeed before landing on my blog, where Google indexed it. By updating one small app on my iPhone, I had left a giant geotagged footprint across the Web.

A few days later I had another disturbing realization. It’s a Tuesday and I’m blowing off a work meeting in favor of a bike ride through Golden Gate Park (37.771558 °N, 122.454478 °W). Suddenly it hits me—since I would later post my route online with the date and time, I would be just a Google search (“Mat Honan Tuesday noon”) away from getting busted. I’m a freelancer, and these are trying economic times. I can’t afford to have the Internet ratting me out like that.

To learn how to deal with this new openness….

And the punch line:

And that’s when it hit me: I had gained better location awareness but was losing my sense of place. Sure, with the proper social filters, location awareness needn’t be invasive or creepy. But it can be isolating. Even as we gradually digitize our environment, we should remember to look around the old-fashioned way. I took a deep breath, pulled back onto the highway, and drove home—directed by the Google Maps app on my iPhone, of course. And I didn’t get lost once.

[Editor's note: And here I thought the Wii was just for bowling, lol.]

Republished from Google Lat Long blog.Thursday, January 8, 2009 at 1:56 PM

This year for Macworld I decided to create a program that allows people to “surf” any region on the Earth’s surface using a Nintendo Wii Balance Board and the Google Earth API. To do this, I used the Google Earth Browser Plug-in with a Javascript API. The Wii Balance Board transmits the your movements to the Earth Surfer application using Bluetooth and allows you to maneuver a virtual milk truck by shifting your balance as if you were on a surfboard.

Check out the following video to see it in action:

While it’s fun to use Earth Surfer, I really wrote it to inspire others to write their own programs. It’s all open source using the Apache License, so you can use the code in your own programs, even commercial ones.

It is based on Thatcher Ulrich’s terrific Javascript Monster Milktruckdemo, which is an open source program on a webpage. I wrapped it as a Macintosh application program so I could add Objective-C. Objective-C uses the Macintosh Bluetooth support to decode the Bluetooth packets from the Wii Balance Board. The Balance Board support is my work. I based that on DarwiinRemote, open source decoders for the Wii Remote.

A mathematician who pioneered a fractal-based urban-mapping technique is embroiled in a copyright battle that raises legal questions about whether a company can claim ownership of the definition of neighborhoods: their specific locations and boundaries. The dispute highlights a growing movement to quantify the amorphous tendrils connecting communities.

Bernt Wahl had the idea in 2004 to use a blend of mathematical modeling and old-fashioned shoe leather to map out unofficial neighborhoods — areas like Bernal Heights in San Francisco, or New Orleans’ French Quarter — whose borders are drawn mostly in the minds of the inhabitants.

Since then, he’s produced maps defining more than 18,000 neighborhoods in 350 U.S. and international cities, which are used in everything from search localization to epidemiology. The Federal Deposit Insurance Corp. is currently using Wahl’s maps to better understand which neighborhoods are being slammed hardest by the mortgage crisis.

Vermont-based mapping company Maponics is now suing Wahl to keep him from creating any more neighborhood maps “derived from or containing parts of” the original maps he produced four years ago, which defined 7,000 neighborhoods in 100 cities. Wahl did that work as a contractor for a real estate web portal, which then sold the copyright to Maponics. Because American’s biggest metropolitan areas were included in the original batch of maps, the lawsuit could effectively bar Wahl from the mapmaking business for good.

The lawsuit highlights the growing importance of neighborhood data in web applications and science. Since Wahl pioneered the industry four years ago, other companies have entered the neighborhood-mapping field, which has swollen into a big part of a $17 billion localized-mapping industry, says Ian White, CEO of San Francisco-based Urban Mapping.

Neighborhood mapping is being used for marketing, siting new retail outlets, social networking, and analyzing crime patterns and earthquake damage. Yahoo announced in June that it had licensed neighborhood-mapping data from Urban Mapping for 2,000 U.S. cities. Earlier this year, Zillow opened its database of 7,000 neighborhoods to the world under a Creative Commons license.

“Everyone made out like a bandit except me,” Wahl says.

Wahl began his work when he was contracted by real estate portal HomeGain to optimize the firm’s search engine. At that time, real estate site maps were organized either by ZIP code or by census tract, which are both fairly arbitrary shapes drawn with disregard for the differences in the neighborhoods within. The Thomas Guides have long noted neighborhoods, but did not attempt to define where they begin and end.

Wahl saw that as a fatal flaw. “Neighborhoods are really important,” he says. “For example, there’s a census tract that combines downtown Berkeley and North Berkeley. In Berkeley hills, the average age is 57, and downtown it’s 24. The incomes and values are completely different. It made me start thinking that we needed a different way to let people look for homes.”

Working with 15 student interns, Wahl began phoning local-government planning departments, chambers of commerce and other community sources in hundreds of cities. “There’s usually a librarian in each place who remembers the neighborhoods — the trick is finding them,” Wahl says. “And you have to be careful about what people tell you, because they can tend to bleed their home into a better neighborhood.”

Using the anecdotal data, Wahl drew polygons that contain the neighborhoods, then tacked them to base maps created by the U.S. Census. The new maps hit big. HomeGain went from limping into its last few million dollars of startup capital to being one of the leading real estate search sites. The company was eventually sold to a consortium of five giant newspaper companies, including the Washington Post.

When HomeGain’s management changed, the new bosses sold Wahl’s first neighborhood map data to Maponics for $40,000. Wahl had permission to keep selling and using the data for six months, according to court documents.

“They gave me $5,000,” Wahl says.

Wahl has continued to develop his data, refining the boundaries on his U.S. maps, and expanding internationally to Asian and European cities in 30 countries. His customers include Craigslist and Ask.com, and he gives away data at no charge to researchers, including those at the FDIC, and to epidemiologists working with the Centers for Disease Control to track the spread of disease.

“We aren’t getting rich off this, though clients do pay for the data,” Wahl says. “We try to get the data out everywhere we can, so we can see how people are using it — that’s very interesting. It’s about public service and the public good as much as making money.”

But the low price tag for Wahl’s maps is precisely what irks Maponics, which accuses Wahl, and his company, Factle, of offering the data at “fire-sale prices.”

Last year, Maponics contacted one of Wahl’s customers, Toursheet.com, and demanded the social place-marking site stop using Wahl’s data. “It allows … Toursheet to use a common map to show the attitude of the neighborhood, so people can have a real sense of community,” says founder Kyle Else. “Well, it did before I heard from Maponics…. They threatened my future development. I missed my window because of their threats, and I’m stuck in limbo until this is sorted out.”

Maponics filed suit in federal court in Los Angeles in November 2007 accusing Wahl of copyright infringement and unfair competition.

“We’re not out to put Bernt out of business,” says George Frost, Maponics’ attorney. “If they’ve got another product that isn’t related to our product, they’re free to sell it. But the software and information that went into it belong to us.”

Maponics CEO Darrin Clement has said in e-mails to Wahl’s customers that Wahl “stole” Maponics data. That’s prompted Wahl to countersue for defamation.

Wahl believes neighborhood boundaries are in the public domain. “I don’t know how anyone can say they own it,” Wahl muses. He argues there’s more at stake than just profits.

“This data literally saves lives,” says Wahl. “We could make more money at other jobs or selling the data for market value, but want we want to do is save lives and save the world. That starts at the neighborhood.”

Cooling the Globe

Many climate specialists see so-called geoengineering techniques as a way to bring down global temperatures if other attempts to combat global warming fail. One approach is to inject sulfur dioxide into the stratosphere, where it reacts to form particles that block sunlight.

Roll over the numbers in the infographic to learn more.

Infographic: Ryan Vulk

It was one of the largest public demonstrations in US history. On June 12, 1982, an estimated 750,000 protesters thronged Central Park in New York City, chanting “No nukes!” and bearing signs reading “Reagan is a bomb — both should be banned” and “Arms are for embracing.” Some demonstrators called for unilateral US disarmament, others for renewing arms control talks with the Soviet Union. It was a diverse coalition that had been pulled together by Ken Caldeira, a 25-year-old activist and computer geek. Back then he was paying the rent doing software consulting on Wall Street, but his passion for the environment would eventually lead him to become one of the nation’s leading experts on global warming.

Around the same time, at the Lawrence Livermore National Laboratory near San Francisco, Lowell Wood — then 41 and a protégé of the brilliant and controversial hydrogen bomb inventor Edward Teller — was leading a secretive team of young geniuses called the O Group. They weren’t merely working with the nukes that Caldeira and his fellow peaceniks reviled; they were dreaming up new and expanded uses for them. One plan called for channeling the energy of a hydrogen bomb into laser blasts that could theoretically destroy enemy ballistic missiles from outer space. It sounded crazy, but Wood and Teller’s ideas inspired President Reagan’s famous March 23, 1983, “Star Wars” speech introducing the Strategic Defense Initiative, the bane of arms-control advocates everywhere.

What’s surprising, then, is that today, 25 years later, Caldeira, the left-wing environmentalist, calls Wood, the Cold Warrior and Star Wars proselytizer, “one of my best friends.” Recently, they have collaborated on strategies for a process known as geoengineering: the large-scale, deliberate modification of the planet to counteract the consequences of ever-increasing concentrations of atmospheric greenhouse gas. The global climate crisis has made for strange bedfellows, and Caldeira’s passage from devout environmentalist to would-be geoengineer has led him into a partnership that his younger self would have scorned.

Geoengineering schemes sound like they’re pulled straight from pulp sci-fi novels: Fertilize the oceans with iron in order to sequester carbon dioxide; launch fleets of ships to whip up sea spray and enhance the solar reflectivity of marine stratocumulus clouds; use trillions of tiny spacecraft to form a sunshade a million miles from Earth in perfect solar orbit. They all may seem impractical, but among a small but growing set of climate scientists, one idea that Wood and Teller started pushing in the late 1990s (before Teller’s death in 2003) is gaining acceptance: Inject sulfur dioxide into the stratosphere to reflect a portion of the sun’s rays back into space, thus cooling the planet.